With respect to vibrations of a vehicle generated by the output torque variation of the vehicle engine, a vibration damping device has been known which actively apply vibrations by causing a vibration application means to generate a vibration damping force in order to damp vibrations of a vehicle. Specifically, as such a vibration damping device, a damping device has been proposed which comprises a linear actuator serving as a vibration application means provided in an engine as a vibration generating source, a means for detecting the number of revolutions of the engine as the vibration generating source, a vibration detecting means for detecting vibrations at the position at which the vibrations are to be damped, i.e., a vibration-damped position, and an adaptive control algorithm for outputting a vibration application force to the linear actuator based on the detected number of revolutions of the engine and the vibrations at the vibration-damped position (see for example, Patent Document 1). In this vibration damping device, a vibration application command having the optimum amplitude and phase can be output by the adaptive control algorithm, in accordance with the number of revolutions of the engine and the vibrations currently detected at a vibration-damped position. As a result, vibrations which are generated from the engine serving as the vibration generating source and are transmitted to positions such as a seat section, in which the vibrations are to be damped, can be reduced by a vibration damping force generated from the vibration application means.
On the other hand, as a linear actuator serving as a vibration application means, a linear actuator has been known in which an elastic supporting portion (a plate spring) holds a movable element at a predetermined position and elastically deforms to support the movable element (see for example, Patent Document 2). Since this linear actuator does not generate wear and slide resistance in the movable element, even after the use for long time, high reliability is obtained without decreasing the accuracy of an axis supporting and the improvement of performance can be obtained without the loss of electric power consumption due to the slide resistance. Further, when the elastic supporting portion is supported by a stator at a position farther than a coil while avoiding the interference with the coil and using the movable element as a base point, it becomes possible to arrange a large coil and the elastic supporting portion closer to each other, whereby miniaturization of the linear actuator can be achieved.
When a vibration damping control is performed to damp vibrations of a target equipment by providing the linear actuator described in the Patent Document 2 with an auxiliary mass (a weight) and using a reaction force generated upon vibrating this auxiliary mass, an amplitude command value and a frequency command value are obtained based on a vibration state of the control target equipment, and a current value, which is applied to the linear actuator, is controlled in accordance with these amplitude command value and frequency command value. Since an attachment of such a vibration damping device to the body of an automobile permits compensation of force, which is applied from the engine to the body of automobile, the vibration of the body can be reduced.